Power semiconductor devices, such as power diodes, power MOSFETs, power IGBTs or power thyristors, are designed to withstand high blocking voltages. Those power devices include a pn-junction that is formed between a p-doped semiconductor region and an n-doped semiconductor region. The component blocks—or is switched off—when the pn-junction is biased in its reverse direction. In this case, a depletion regions or space charge zone propagates in the p-doped and n-doped regions. Usually one of these semiconductor regions is more lightly doped than the other one of these semiconductor region, so that the depletion region mainly extends in the more lightly doped region, which mainly supports the voltage applied across the pn-junction. The semiconductor region supporting the blocking voltage is referred to as base region in a diode or thyristor, and is referred to as drift zone in an MOSFET or IGBT.
The ability of a pn-junction to support high voltages is limited by the avalanche breakdown phenomenon. As a voltage applied across a pn-junction increases, an electric field in the semiconductor regions forming the pn-junction increases. The electric field results in acceleration of mobile carriers present in the semiconductor region. An avalanche breakdown occurs when, due to the electric field, the charge carriers are accelerated such that they create electron-hole pairs by impact ionization. Charge carriers created by impact ionization create new charge carriers, so that there is a multiplication effect. At the onset of avalanche breakdown, a significant current flows across the pn-junction in the reverse direction. The voltage at which the avalanche breakdown sets in is referred to as breakdown voltage.
The electric field at which the avalanche breakdown sets in is referred to as critical electric field. The absolute value of the critical electric field is mainly dependent on the type of semiconductor material used for forming the pn-junction, and is weakly dependent on the doping concentration of the more lightly doped semiconductor region.
The critical electric field is a theoretical value that is defined for a semiconductor region that has an infinite size in directions perpendicular to field strength vectors of the electric field. Power semiconductor components, however, have semiconductor bodies of finite size that are terminated by edge surfaces in lateral directions. Due to different reasons, such as imperfections of the crystal lattice at the edge surfaces, the breakdown voltage of the component is reduced in edge regions that are close to the edge surfaces compared to inner regions that are distant to the edge surface. In order to compensate for the reduced breakdown voltage in the edge regions edge terminations are known that serve to reduce the electric field in the regions compared with the inner regions.
Different types of edge terminations are known. So-called vertical edge terminations or mesa terminations, respectively, include specific geometries of the edge surfaces or passivation layers on the edge surfaces. Bevel edge terminations have edge surfaces that are beveled. Bevel edge terminations are, in particular, effective in reducing the electric field in edge regions of semiconductor components that have circular-shaped semiconductor bodies. This is the case when the semiconductor body of the component corresponds to a complete wafer. However, problems in terms of a reduced breakdown voltage in the edge region may occur when the semiconductor body has a rectangular form, like a rectangular form that results from separating a wafer into several semiconductor bodies or dies, respectively.
There is therefore a need for an improved edge termination for semiconductor components, in particular semiconductor components having a semiconductor body with a rectangular geometry.